Creeping indigo (Indigofera spicata and Indigofera hendecaphylla)

Datasheet

Description

Click on the "Nutritional aspects" tab for recommendations for ruminants, pigs, poultry, rabbits, horses, fish and crustaceans

Creeping indigo (Indigofera hendecaphylla), habit, Maui, Hawaii, USA

Creeping indigo (Indigofera spicata), habit, Florida, USA

Creeping indigo (Indigofera spicata], inflorescence, Florida, USA

Creeping indigo (Indigofera spicata), pods, Maui, Hawaii, USA

Common names

Trailing indigo, creeping indigo, indigo, spicate indigo [English], indigo rampant, indigotier rampant [French]; iniko, inikoa, indigo, kolu [Hawaiian]; basingan [Indonesian]; amendoim-bravo [Portuguese]; añil rastrero [Spanish]

Species

Indigofera hendecaphylla Jacq. ; Indigofera spicata Forssk. [Fabaceae]

Synonyms

Indigofera endecaphylla Lam., Indigofera hendecaphylla Lam.

Taxonomic information

Since 1993, Indigofera hendecaphylla and Indigofera spicata are considered to be separate species. Before 1993, they were considered to belong to the same taxon, usually Indigofera spicata (Du Puy et al., 1993). Consequently, in scientific literature written prior to that date, the names Indigofera spicata, Indigofera hendecaphylla and Indigofera endecaphylla may refer either to Indigofera spicata or to Indigofera hendecaphylla. Both species are now sometimes referred to as the "Indigofera spicata complex" (Ossedryver et al., 2013).

Related feed(s)

Description

Creeping indigo (Indigofera spicata Forssk. and Indigofera hendecaphylla Jacq.) is a perennial legume grown in tropical and subtropical regions mostly as a cover crop and for green manure. Highly palatable and nutrient-rich, it was once considered as a potentially valuable fodder but the toxicity of certain varieties for all livestock species led to its abandonment. Creeping indigo is still used for pasture in East Africa.

Morphology

Creeping indigo has a creeping or weakly ascending habit. Its stems, arising from a central basal crown, can be 1 m long and grow to a height of 0.5 m. Creeping indigo has a deep woody taproot. Its stems are green, pubescent and somewhat flattened when young, and become brown in colour when they get older. The leaves are alternate and pinnately compound, 12-40 mm long, with alternately arranged leaflets that are dull green at their upper surface. The inflorescences are arranged in erect, spike-like racemes, salmon pink to red-orange in colour. The flowers are papillionaceous, 3-4 mm long. The fruits are linear-oblong pods, 10-18 mm long x 1.5-2 mm wide, borne in dense descending clusters. They are dehiscent and contain 4-8 cuboid, smooth seeds (Cook et al., 2005; Du Puy et al., 1993). Indigofera spicata and Indigofera hendecaphylla were considered to be the same species until 1993 and are morphologically close, though Indigofera spicata has shorter pods and inflorescences, and a lower number of leaflets per leaf (Du Puy et al., 1993).

Utilisation

Creeping indigo is mainly planted as green manure and as a cover crop in coffee, tea or rubber plantations. It is very palatable to livestock (except pigs) and has been reported to be used for fodder in East Africa and India. Indigofera spicata was mentioned as a pasture species in Ethiopia as recently as 2014 (Bezabih et al., 2014). It was once considered to be a promising fodder able to form well-balanced mixtures with grasses. However, in the 1940-1950s, feeding trials and field observations in the USA demonstrated that the plant was toxic for cattle, sheep, rabbits, pigs, Guinea pigs, horses and chicks, so attempts to use it as fodder were abandoned (see Potential constraints on the "Nutritional aspects" tab) (Emmel et al., 1941; Freyre et al., 1952; Nordfeldt et al., 1952; Morris et al., 1954; Morton, 1989). There is also a report that the plant was once used for forage in East Africa and then abandoned after it was found to be toxic (Morton, 1989). In Australia, creeping indigo was imported as potential pasture legume but rejected for this purpose after its toxicity was recognised (Aylward et al., 1987). Creeping indigo used to be a source of dye but is now replaced by synthetic dyes (Sunarno, 1997; Duke, 1981).

Due to the confusion between Indigofera spicata and Indigofera hendecaphylla in pre-1993 studies, properties once attributed to Indigofera spicata, notably its toxicity and invasiveness, may actually concern only Indigofera hendecaphylla (Sunarno, 1997). At the time of writing (December 2014), such differences are far from clear due to the lack of recent literature. It may be possible that African strains of Indigofera spicata, which are still used for fodder in their native range, are valuable fodder and would deserve attention (Sunarno, 1997), but Indigofera spicata plants have been considered toxic to livestock in Australia (Ossedryver et al., 2013).

Distribution

The origin of creeping indigo is debated. It is thought to have originated in Africa, Madagascar, South and South-East Asia and then have spread to, and naturalised, in most tropical regions (CABI, 2014). Indigofera hendecaphylla is a widespread pantropical species, distributed throughout the Old World tropics and subtropics to the Pacific Islands, often in more humid areas. Indigofera spicata is confined to Africa, Yemen, Madagascar and the Mascarene Islands, often in the drier regions (Du Puy et al., 1993; Sunarno, 1997). Creeping indigo can be naturally found in disturbed grasslands, cultivated places and degraded areas including roadsides or paths. It grows from sea level up to an altitude of 2700 m, and in places where annual rainfall ranges from 600 to 1500 mm with an average annual temperature between 13°C and 27°C. Creeping indigo can grow on a wide range of soils including those with a low pH or deficient in phosphorus. It can withstand drought and an annual rainfall as low as 200 mm, but it also does well under heavy rain with up to 4000 mm annually (Cook et al., 2005; Morton, 1989; Duke, 1981). Creeping indigo prefers full light. It can grow well under light shade but grows poorly under heavy shade, for instance in rubber plantations (Sunarno, 1997).

Forage management

Creeping indigo is often cultivated in mixed stands with legumes such as Caribbean stylo (Stylosanthes hamata), Stylosanthes scabra, Stylosanthes seabrana, Desmodium triflorum or Chamaecrista rotundifolia. It can be sown with grasses like carpet grass (Axonopus fissifolius), Bermuda grass (Cynodon dactylon) or Pangola grass (Digitaria eriantha) (Cook et al., 2005). Creeping indigo can either be sown or propagated through stem cuttings. As the percentage of hard seeds is very high, scarification (mechanical or chemical) is necessary before sowing. The seeds can also be inoculated with appropriate rhizobia for future N fixation. They should be mixed with sand or dry soil for better distribution during sowing operations. The seeds should not be sown deeper than 1 cm deep (Sunarno, 1997). When propagation is done through cuttings, five cuttings are planted in holes made in the soil at a spacing of 60 cm x 60 cm. A good cover can be obtained within 4-6 months. When the cover is obtained from cuttings, the height seldom exceeds 12 cm. When it is obtained from seedling, trailing stems can be as long as 2-3 m and the stand can reach 30-40 cm high after 2 years (Sunarno, 1997). Creeping indigo is said to be unaffected by any serious diseases or pests (Duke, 1981).

Environmental impact

Invasiveness

Creeping indigo has become invasive in many areas where it was introduced as a forage or cover crop, for instance in Puerto Rico and Southern Florida (Morton, 1989). Because it is highly palatable to herbivores, livestock may be poisoned after eating large amounts of the legume.

Cover crop, green manure and erosion control

The main usage of creeping indigo is as a cover crop or green manure for soil enrichment (Sunarno, 1997). Its creeping habit also makes it useful for controlling erosion effectively on hilly and undulating land even under heavy rainfall. It is considered more effective than Clitoria ternatea. A well-established cover of creeping indigo is hardly penetrable by weeds (Sunarno, 1997). In Malaysia, it used to be planted for erosion control and soil enrichment in tea plantations, where the fact that it did not climb trees was appreciated (Morton, 1989).

Nutritional aspects

Nutritional attributes

There are very few data about the composition of creeping indigo. Early studies in Hawaii and Puerto Rico reported poor (13% protein, 33% crude fibre, Nordfeldt et al., 1952) to good values (19.5% protein in the DM, Telford et al., 1947). However, an Australian study found a high protein content of 25% DM (Hutton et al., 1958), with a more recent Ethiopian study reporting a protein content of 23% DM and a low NDF content (35% DM) (Bezabih et al., 2014). Maturity and the leaf:stem ratio probably influenced the nutritional value.

Potential constraints

Toxicity

Creeping indigo has been reported to be highly toxic to animals. Like many Indigofera species, all parts of the plant, including leaves and seeds, contain indospicine, a non-protein amino acid, a thermostable antagonist of arginine and an inhibitor of protein synthesis (Hutton et al., 1958; Hegarty et al., 1968; Christie et al., 1975; Strickland et al., 1986). Indospicine causes liver lesions in rats, rabbits, sheep, horses and cattle as well as abortion in mammals (Hutton et al., 1958; Salam Abdullah et al., 1997; Sunarno, 1997; Morton, 1989; Aylward et al., 1987; Christie et al., 1975; Ossedryver et al., 2013). The lethal dose in 1-week-old chicks is 5 g of dry plant material (Morris et al., 1954). Cattle were susceptible to creeping indigo poisoning when the diet contained more than 50% of creeping indigo (Nordfeldt et al., 1952). Guinea pigs fed for 290 days on a creeping indigo failed to reproduce due to systematic abortions (Freyre et al., 1952).

Because of the confusion surrounding the taxonomy of these plants, it remains difficult to know which species of the "Indigofera spicata complex" was actually found toxic in the studies cited above. It is probable that the species implicated in livestock poisoning in past studies was Indigofera hendecaphylla rather than Indigofera spicata (Wilson et al., 2008). Although some varieties of creeping indigo, especially those from Africa (which may be Indigofera spicata), were reported to provide valuable and palatable fodder (Sunarno, 1997), while in Australia Indigofera spicata has since been found to cause poisoning in ponies. This confirms that both species may contain harmful almounts of indospicine (Ossedryver et al., 2013).

In addition to indospicine, the leaves and stems (but not the seeds) of plants of the Indigofera spicata complex contain another toxic component, 3-nitropropionic acid (3-NPA). Poultry are particularly susceptible to 3-NPA found in creeping indigo (Britten et al., 1963).

Ruminants

Information on the use of creeping indigo for ruminant feeding is scarce. A series of trials that began in Hawaii in the late 1930s showed that it was very palatable to cattle. In 10 years of short-interval pasture trials with relatively small proportions of the legume, no adverse effects were noted in young cattle. It was only when the concentration of the legume exceeded about 50% of the forage (due to feed shortages) that toxicity symptoms began to appear in heifers and dairy cows. Trials with sheep also demonstrated its toxicity when ingested in large amounts (Nordfeldt et al., 1952). Since the use of creeping indigo was discontinued in the USA, little work has been done to study its value as forage, even though it appears to be still used for pasture in other countries, and notably in East Africa. In Kenya, creeping indigo was among the grazing plants most preferred by goats (Osolo et al., 1994). In Ethiopia, Indigofera spicata was included in a comparison of the nutritive value of grazing species. OM digestibility and ME values estimated by the gas production method were 67% and 9.0 MJ/kg DM respectively (Bezabih et al., 2014).

Pigs

Creeping indigo is highly unpalatable to pigs (Nordfeldt et al., 1952).

Poultry

Creeping indigo is toxic to poultry, who are susceptible both to indospicine and 3-NPA. The lethal dose in 1-week-old chicks is 5 g of dry plant material (Morris et al., 1954).

Rabbits

Creeping indigo should not be fed to rabbits. Its toxicity to rabbits has been known since the 1940s (Emmel et al., 1941). Green or dried leaves and seeds are relatively palatable to rabbits but clearly toxic. Rabbits died with severe liver damages 5 to 30 days after consuming fresh creeping indigo leaves for only few days (spontaneous intake of 50 g/d for rabbits weighing 2-3 kg), or after consuming a diet containing 50% seeds for 1 or 2 days. Dried and cooked pellets containing 50% creeping indigo leaves were unpalatable to rabbits, but when they were fed alternately with a regular diet, thus reducing the average daily intake of indospicine, survival increased up to 84 days (Hutton et al., 1958). As observed with cattle in Hawaii, where prolonged but limited intake of creeping indigo was not found detrimental to health (Nordfeldt et al., 1952), it is possible that rabbits tolerate a small proportion of creeping indigo in their diets. Nevertheless, until it is demonstrated that creeping indigo can be used safely in rabbit feeding, its use should be strongly discouraged.

Horses and donkeys

Grazing creeping indigo has been linked to horse poisoning. In Southern Florida, several occurrences of central nervous system disturbances in horses, termed "grove poisoning", were reported when grazing Indigofera hendecaphylla (Morton, 1989). In Australia, ponies grazing a pasture containing 24% Indigofera spicata (fresh basis) showed severe symptoms of poisoning and had to be euthanized (Ossedryver et al., 2013). An early trial in the Philippines comparing groundnut hay and creeping indigo hay concluded that the latter was less palatable (Fajardo, 1934).

Nutritional tables

Tables of chemical composition and nutritional value

Creeping indigo (Indigofera spicata and Indigofera hendecaphylla), aerial part, fresh

Avg: average or predicted value; SD: standard deviation; Min: minimum value; Max: maximum value; Nb: number of values (samples) used